In recent years, practical use of a home network where digital devices at home are mutually connected such that users can enjoy contents of high image quality and high audio quality have been turning into reality. For example, the High-Definition Multimedia Interface (HDMI) which was standardized in December 2002, is a standard for digital audio-video input/output interface used in next generation audio-visual (AV) devices. The standard allows transmission of audio, video, and controls signals with one cable (for example, see Non-Patent Reference 1).
The HDMI standard defines Consumer Electronics Control (CEC) as a protocol for transmitting the control signals bidirectionally. The CEC protocol allows controlling multiple AV devices with one remote-controller by relaying the control signals among devices. To put it differently, bidirectional transmission of the control signals among a television (TV), an AV amplifier, and a DVD player/recorder allows controlling the entire home theater with one remote controller.
The HDMI standard has features including, not only preventing deterioration of the signals by digital transmission, but preventing unauthorized copying. In order to achieve the feature, reproduction devices such as the DVD player/recorder read the reproduction capability of a connected device to adjust output format of the audio-video data and encrypts the audio-video data and transmits the encrypted data.
The reproduction capability information is transmitted from a device such as a TV or an AV amplifier having an HDMI input port (hereinafter referred to as “HDMI input device”) to the connected device (hereinafter referred to as “HDMI output device”) using a Display Data Channel (DDC) bus which is a unidirectional data connection. The DDC is a standard by the Video Electronics Standards Association (VESA) defining a function to transmit information such as type information of a display to the connected device in order to implement plug and play of the display. The type information of the display and the audio formats and video formats that are supported are stored in the memory in the HDMI input device as Enhanced Extended Display Identification Data (EDID). The EDID is read from the HDMI output device connected to the DDC bus via the DDC bus in response to switching of the Hot Plug Detect Signal (HPD) from low to high (or an HPD pulse) by the HDMI input device. When the HPD is high, the HDMI output device can read the EDID of the HDMI input device, and this suggests that the HDMI input device such as the TV or the AV amplifier has a capability to reproduce the digital audio-video data in the audio-video format indicated by the EDID.
Meanwhile, the HDMI standard also adopts the High-bandwidth Digital Content Protection System (HDCP) which is an authentication protocol for confirming, when outputting the contents that require copyright protection, that the connected device is valid. The HDCP defines that the authentication starts in response to the switching of the HPD from low to high (or an HPD pulse).
The function to adjust the data output format after the reproduction device reads the reproduction capability information of the connected device is useful. However, there is a disadvantage that each time the audio reproduction capability changes due to a change in the device to output audio (speakers) among the HDMI output devices connected to the reproduction devices, for example, the HDMI output device connected to the reproduction device switches the reproduction capability information read by the reproduction device, so that the reproduction device outputs the appropriate audio data.
FIG. 1 illustrates an example configuration of an HDMI connection.
For example, the DVD recorder 10, the AV amplifier 20, and the TV 30 are connected.
The DVD recorder 10 includes one HDMI output port (10PO_1), the AV amplifier 20 includes one HDMI input port (20PI_1) and one HDMI output port (20PO_1), and the TV 30 includes one HDMI input port (30PI_1).
The DVD recorder 10, the AV amplifier 20, and the TV 30 are respectively connected via the HDMI, and the audio-video data is transmitted unidirectionally from (10PO_1), (20PI_1), (20PO_1), and to (30PI_1), in that order. The control messages are transmitted bidirectionally on the control signal bus of the HDMI. Here, regarding audio output, it is assumed that the AV amplifier 20 is capable of outputting 5.1-channel Pulse Code Modulation (PCM), the TV 30 only supports 2-channel PCM output, and the DVD recorder 10 reproduces DVD video contents compliant with 5.1-channel digital surround. A state where the TV 30 outputs both the video and the audio is referred to as a “television mode”, and a state where the TV 30 outputs the video and the AV amplifier 20 outputs the audio is referred to as a “theater mode”. The TV 30 instructs the AV amplifier 20 to switch the television mode and the theater mode via the CEC protocol, using the device operation by the user as a trigger for the switching. However, detailed explanation is omitted since the switching is not a focus of the present invention.
FIG. 2 illustrates an example of audio output in the television mode.
Since the TV 30 can only reproduce audio in 2-channel PCM, the audio reproduction capability information 30C1 described on EDID 30C of the TV 30 is set as follows, for example, “audio type=PCM, the maximum number of channels=2”. The EDID 30C sets sampling frequency and the number of quantized bits that are supported, and regarding the video, supported types of the video formats as the reproduction capability information, however, detailed explanation is omitted since they are not the focus of the present invention. The HPD signal 30P which is outputted by the TV 30 to the AV amplifier 20 is set to be high.
Here, in the case of the television mode where the TV 30 outputs both audio and video, the audio reproduction capability information 20C1 described in the EDID 20C of the AV amplifier 20 is set as “audio type=PCM, the maximum number of channels=2”, adjusted to the audio reproduction capability information 30C1 of the TV 30, which has been read out of the TV 30. Although the AV amplifier 20 is capable of performing 5.1-channel surround reproduction, when the reproduction of 2 channels or more is set in the audio reproduction capability information 20C1, the TV 30 that can only reproduce the 2-channel PCM cannot reproduce the audio properly upon multi-channel audio reproduction from the DVD recorder 10. The HPD signal 20P which is outputted by the AV amplifier 20 to the DVD recorder 10 is set to be high.
The DVD recorder 10 reads the EDID 20C from the AV amplifier 20, and transmits the audio in 2-channel PCM that the TV 30 can output, based on the audio reproduction capability information 20C1.
FIG. 3 shows a conventional example of the audio-video data reproduction method in the HDMI connection.
During the television mode where the TV 30 outputs the audio and the video, the audio reproduction capability information 30C1 of the TV 30 and the audio reproduction capability information 20C1 of the AV amplifier 20 are same as those shown in FIG. 2.
Here, when switching to the theater mode where the AV amplifier 20 outputs the audio (30H), the audio output from the AV amplifier 20 is limited to 2 channels if the audio reproduction capability information 20C1 of the AV amplifier 20 remains unchanged from the television mode. Thus, the AV amplifier 20 temporarily switches the HPD signal 20P to low (20P_L), sets the audio reproduction capability information 20C2 indicating that the AV amplifier 20 is capable of 5.1-channel reproduction (for example, “audio type=PCM, and the maximum number of channels=6), and switches the HPD signal 20P to high (20P_H) again.
When the HPD signal 20P is switched from low (20P_L) to high (20P_H), the DVD recorder 10 determines, compliant with the HDCP, that there is a possible change in the HDMI connection status, and starts authentication again in order to confirm that the connected device is valid or not. When starting the authentication, the DVD recorder 10 stops outputting the audio-video data, reads the EDID 20C from the AV amplifier 20 again, and confirms whether the AV amplifier 20 is valid or not while transmitting video signals that does not require contents protection (for example, blackouts). Subsequently, when the AV amplifier 20 is confirmed as valid, the DVD recorder 10 starts outputting the audio-video data again, and with regard to the audio, the DVD recorder 10 starts outputting the audio in the audio reproduction format that the AV amplifier 20 is capable of reproducing, indicated by the audio reproduction capability information 20C2 of the AV amplifier 20. Detailed explanation for the HDCP authentication is omitted since it is not the focus of the present invention.
Another example with a different HDMI connection configuration is described as follows.
FIG. 4 illustrates an example configuration of the HDMI connection.
For example, it is assumed that the DVD recorder 10, the AV amplifier 21, and the TV 31 are connected.
The AV amplifier 21 includes one HDMI output port (21PO_1) and one optical digital audio input (21PI_1), and the TV 31 includes two HDMI input ports (31PI_1, 31PI_2), and one optical digital output (30P0_1).
The configuration in FIG. 4 is different from the configuration in FIG. 1 in that the DVD recorder 10 is connected to the HDMI input port (31PI_1) in the TV 31 instead of the AV amplifier 21, and the optical audio digital cable connects the TV 31 and the AV amplifier 21.
The audio-video data is unidirectionally transmitted from (10PO_1) to (31PI_1). The audio data is further transmitted from (31PO_1) to (21PI_1). The control messages are bidirectionally transmitted on the control signal bus of the HDMI. Here, it is assumed that regarding of audio output, the AV amplifier 21 is capable of outputting 5.1-channel compressed audio (for example, Dolby Digital (registered trademark) audio), and the TV 31 only supports 2-channel PCM output.
FIG. 5 illustrates an example of audio output in the television mode.
Since the TV 31 can only reproduce audio in 2-channel PCM, the audio reproduction capability information 31C1 contained in the EDID 31C of the TV 31 is specified as follows, for example, “audio type=PCM, the maximum number of channels=2”. The HPD signal 31P which is outputted by the TV 31 to the DVD recorder 10 is set to be high.
The DVD recorder 10 reads the EDID 31C of the TV 31, and transmits the audio in 2-channel PCM that the TV 31 can output, based on the audio reproduction capability information 31C1.
FIG. 6 shows a conventional example of the audio-video data reproduction method in the HDMI connection.
During the television mode where the TV 31 outputs the audio and the video, the audio reproduction capability information 31C1 in the TV 31 is same as the one shown in FIG. 5.
Here, when switching the audio to the theater mode where the AV amplifier 21 outputs the audio (31H), the audio output from the AV amplifier 21 is limited to 2 channels if the audio reproduction capability information 31C1 in the TV 31 remains unchanged, since the audio output from the DVD recorder remains in the 2-channel PCM.
Thus, the TV 31 temporarily switches the HPD signal 31P to low (31P_L), sets the audio reproduction capability information 31C2 indicating that the AV amplifier 21 is capable of 5.1-channel reproduction (for example, “audio type=Dolby Digital, and the maximum number of channels=6”), and switches the HPD signal 31P to high (31P_H) again.
When the HPD signal 31P is switched from low (31P_L) to high (31P_H), the DVD recorder 10 determines, compliant with the HDCP, that there is a possible change in the HDMI connection status in the same manner as the example in FIG. 3, and starts authentication again in order to confirm that the connecting device is valid or not. When starting the authentication, the DVD recorder 10 stops outputting the audio-video data, reads the EDID 31C of the TV 31 again, and confirms whether the TV 31 is valid or not while transmitting video signals that does not require contents protection (for example, blackouts). Subsequently, when the TV 31 is confirmed as valid, the DVD recorder 10 starts outputting the audio-video data again, and with regard to the audio, the DVD recorder 10 starts outputting the audio in the audio reproduction format that the AV amplifier 21 is capable of reproducing, indicated by the audio reproduction capability information 31C2 of the TV 31.    Non-Patent Reference 1: High-Definition Multimedia Interface Specification Version 1.3